The invention disclosed broadly relates to the field of rotating media mass storage devices, and more particularly relates to the field of recording servodata on hard disk drives.
In disk drives, the track density is a predetermined function for each product family. The tolerances of the heads, magnetic variations of the media, and variations in mechanical input noise are all taken into account when setting the track pitch (component parameters). Increased storage can be accomplished by increasing the track density. In the current servowriting process used in manufacturing of disk drives the track density is determined for a product family and is not customized for each individual drive manufactured.
Recording System Overview
In a recording system as shown in FIG. 1, a rotating media 102 and a data head 106, which typically consists of a separate read 152 and write 154 elements, are used to store data in roughly concentric tracks on a storage medium. The head is positioned onto the data tracks 112, 114 by reading sector servo patterns 110, converting them into a voltage signal using read write interface card 124 and amplitude demodulator 140. The output of the demodulator is digitized using A/D converter 142 and input to a microprocessor 144 which is executing a servo control program. The processor calculates a control voltage which is output to DAC 146, converting the value of the control voltage into an analog signal which is input to a VCM driver 148 producing a current which moves the actuator 150 via the voice coil motor (VCM) 108 to position the data head onto the data track. The sector servo patterns are written during the manufacture of the disk drive assembly and are typically spaced at equal angular intervals along the data track. Track densities of modern disk drives are in the range of 10,000 up to 30,000 tracks per inch, so precise placement of the servo tracks is required to define the location of the data tracks.
Sector servo and Data Tracks
In a recording system, the media are servo written with sector servo tracks to allow positioning of the recording head at a radial location, indicated by a track number. An expanded view of a sector is shown in FIG. 2. The sector field consists of servo patterns which in this example are labeled A, B, C, and D and repeat across the surface of the disk. The servo bursts define the center of the servo tracks, and in the example shown there are two servo tracks for each data track. The read element 202 reads the servo bursts A and C, and produces a signal amplitude which is demodulated to create a voltage proportional to the overlap of the head to the servo burst. The difference of the two amplitudes Axe2x88x92C, is input to the microprocessor 144 which computes a control current to the DAC 146 to move the data head 106 to maintain a difference of zero and center the read element 202 on the data track. For example when the signal amplitude of the A burst 204 on Servo Track 1 is equal to the signal amplitude of the C burst 208 on Servo Track 3, then the read element (202) is centered on Data Track 1 (216).
The spacing or track pitch of the servo tracks shown as Servo Track Pitch 212, determines the track pitch of the data tracks. In this case the Data Track Pitch 214 is twice that of the Servo Track Pitch. One of the determining factors in setting the pitch is the tolerance of the heads. For example in modern heads in which the magnetoresistive read and inductive write transducers are separate elements, the tolerances are given for each element as shown below.
The pitch would typically be set to insure that when writing Data Track 1 (216) the write element does not overlap Data Track 2 (218) and overwrite the previously written track which can result in a loss of data. To achieve this, the track pitch is set to exceed the width of the widest write head in the population of write heads used for the disk drive program to insure a gap 220 between adjacent data tracks. In this example the widest write width is 2.9 microns. In addition, magnetic and mechanical inputs which limit the ability of the read head to stay centered on the data track, which are commonly referred to as track misregistration, are part of the statistical calculation performed in setting the track pitch for the product. Today, products have a defined track pitch which is used for all the disk surfaces and drives manufactured, and do not adapt the track pitch for each individual surface or drive manufactured based on drive components such as the read or write heads, spindle bearings, etc. (component parameters) or track misregistration, magnetic performance, etc. (system parameters).
Briefly, according to the present invention there is provided a method of measuring the gaps between adjacent tracks in a recording system during servowriting and allowing the setting of the servo track pitch based on the component or system parameters of individual drives thereby overcoming a limitation of the statistical method of setting track pitch.